Devices that can treat tissue non-invasively are extensively used to treat numerous diverse skin conditions. Among skin treatment applications, non-invasive energy delivery devices may be used to tighten loose skin for making a patient appear younger, to remove skin spots or hair, or to kill bacteria. Such energy delivery devices emit electromagnetic energy with wavelengths distributed across the breadth of the electromagnetic spectrum, and include ultraviolet, visible, and infrared light, both incoherent and coherent; microwave and radio-frequency (RF) energy; as well as sonic and mechanical energy sources.
In particular, high frequency energy delivery devices may be used to treat skin tissue non-ablatively and non-invasively by passing high frequency energy through a surface of the skin. The high frequency energy heats tissue beneath the epidermis to a temperature sufficient to denature collagen, which is believed to cause the collagen to contract and shrink and, thereby, tighten the tissue. The skin is actively cooled to prevent damage to a skin epidermis layer proximate to a treatment tip of the device. Treatment with high frequency energy may also cause a mild inflammation in the tissue. The resultant inflammatory response of the tissue may cause new collagen to be generated over time, which increases tissue contraction.
Conventional treatment tips used in conjunction with such high frequency energy delivery devices effectively distribute the high frequency energy for uniform delivery across a surface of the tip. The uniform energy delivery minimizes locally hot spots on the tip that could cause patient burns despite the use of active cooling. However, some tissue types respond best to treatment when heat is delivered deep into the tissue. Other tissue types respond best when heat is delivered at a shallower depth into the tissue. The depth and/or dose of energy may be controlled by changing the frequency, by adjusting the power of the high frequency generator powering the energy delivery device, or by adjusting the amount of tissue cooling. Although these adjustments may alter the treatment depth of the energy delivered to the tissue, each approach has certain disadvantages and drawbacks that limit their application.
The depth and/or dose of energy may also be controlled by switching treatment tips to change the characteristics of an emitted electric field that delivers the energy to the tissue. However, switching treatment tips is a time consuming and inconvenient approach for changing the treatment depth. Moreover, switching treatment tips significantly increases treatment costs because a clinician must purchase and stock multiple different treatment tips each capable of emitting a different electric field for changing the treatment depth.
What is needed, therefore, are apparatus and methods for overcoming these and other disadvantages of conventional apparatus and methods for selectively adjusting the depth at which high frequency energy is delivered into tissue during non-invasive tissue treatments.